Orfanidis EQ
"de-cramped" parametric equalizer
DESCRIPTION
Based on S. J. Orfanidis' 1997 paper "High-Order Digital Parametric Equalizer Design". This filter has very low CPU usage, zero latency and will maintain a much better frequency response close to Nyquist than conventional "cookbook" EQs.
I have implemented the Matlab-Code from Orfanidis' paper in Reaktor and realized the filter as an IIR Direct Form I structure.
The Reaktor Ensemble file serves as a testing ground and is internally optimized for readability. It can be used like any parametric EQ. The "Asym" button switches the bandwidth gain between geometric mean and arithmetic mean, which will create an asymmetrical boost/cut. The filter has a constant-Q behaviour by default but Gain & Q can be linked together with the "PQ" button. When the gain is set to 0 the filter will also be bypassed. This protects against accumulated rounding errors and NaNs.
The included Reaktor Core Macro is optimized for low CPU usage and can be used to implement this type of filter in your own structures. The macro will run with 64bit precision by default.
Note: there can be some weirdness with very low Q values and an fC close to Nyquist.
###Changelog###
0.7: added automatic filter bypass at Gain=0
0.6: increased precision to 64bit
0.5: added parametric Q button & included optimized Core macro
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